Team Gushue Highway Extension

The Newfoundland and Labrador Ministry of
Transportation and Works requested a TechSpan concrete arch culvert constructed
over the Waterford River to support a 19 m high embankment for the Team
Gushue Highway Extension.

Named in honour of the 2006 Olympic Gold medalist curling team, the Team
Gushue highway once completed will provide a vital link to the NW Avalon
Peninsula. The highway is designed to relieve traffic congestion on all
major routes in the region, and when finished, will connect the Outer Ring
Road in the north with Robert E. Howlett Memorial Drive to the south.

The Waterford river crossing was a major technical and construction challenge
on this project. The 10 m wide river runs in a 19 m deep meandering gorge
and has a swift current, making work in and around the river challenging.
Access to the site was extremely difficult. Two very steep grade construction
roads on each side of the river connected by a temporary bridge provided
access to the bottom of the gorge and the erection site. A temporary diversion
of the river permitted for excavation and site casting of two 5.35 m wide
footings and the erection of the concrete arch culvert in the dry. The
63m long, 11m span, 4m high concrete arch structure supports 19 m of overburden
and the highway road base, allowing the highway a level crossing of the
gorge and river.

The Waterford river crossing structure was not considered in great detail
until just before the project was under review for Environmental Approval.
The initial hydrology study indicated an arch pipe would suffice hydraulically
and be comparable to upstream structures on the river. The initial structure
was conceived to be longer but in order to lessen the footprint of the
structure to have a lesser impact on the river, the structure was shortened
and headwalls were increased to retain more fill. Further changes were
made during construction to make the constructability smoother so the location
of the structure and wall configuration was again revised resulting in
the final configuration.

The precast arch extension is an 11 m span with an internal rise of 4 m
and a thickness of 0.25 m. The earth cover over the crown to highway is
approximately 16.5 m with the side slope on the embankment. The principle
concept depends on the development of a finite element program based on
funicular curve theory for which the bending moment at any point is zero.
The arch is a 3 hinged arch shape that minimizes tensile stress in the
concrete. The design of the arch considers all loads anticipated on the
arch elements during transportation, erection, and backfilling and in-service.

The pre-cast concrete arch shape was calculated by a finite element method
and formed in special flexible moulds to fit the existing shape of the
structure and MSE walls were used as the wing walls and head walls while
the structures were designed to sustain the high overburden. The innovation
of pre-cast concrete arch is to utilize a pre-cast product with a sophisticated
and individual design approach incorporating the optimum arch geometry
and individually suited to the various loading situation for unique structures
like this.

The pre-cast arch used on this project is the TechSpan® product by Reinforced
Earth Company Ltd. and is built by assembling prefabricated concrete elements
in a staggered and symmetrical way to allow a fast installation without
disrupting the traffic below.

The governing phenomenon in the behaviour of an earth-filled precast arch
is the relative stiffness of the concrete structure compared with the soil
behind it. For a precise analysis of the behaviour of the concrete arch,
in relation to the fill during backfilling and in its service stage, a
finite element analysis is required. The state-of-the art design program
developed by RECo uses a finite-element-method to optimize the arch shape
and minimize the bending moments in the concrete. The use of a FEM program
is commonly considered to be the most effective way to analyze the soil
and structure interaction of buried arches.

The analysis includes all of the various load cases which include stripping
& handling during fabrication, transportation, installation, backfilling
and rail surcharge on final fill condition. Based on the most critical
load cases for all combinations, the arch was optimized for both thickness
and rebar design for the required design codes and specifications.